I'm really not sure what the correct terminology is, so I'll do my best to describe it. I've seen this before when part or all of a polygon is "flipped", or its sides cross one another. C2 expects the polygon to have a solid shape. For example, you can't do things like take a square collision polygon, and switch its top two corners (or any two corners for that matter), because the polygon would not be a single solid shape. From what I gather, your polygon doesn't actually have crossing sides, but I'm guessing you accidentally turned the original polygon "inside out", or you switched the position of some of the collision points.
I'd suggest trying to "revert" the collision points. If that doesn't work, try reimporting the image (I believe the collision polygon will be reset), or post your capx so we can take a look.zatyka2013-04-25 04:34:50